Constantine IV of Byzantium

Constantine IV of Byzantium (652-14 September 685) was the Emperor of the Byzantine Empire from 668 to 685, succeeding Constans II of Byzantium and preceding Justinian II of Byzantium.

Biography
Constantine was born in 652 to Constans II of Byzantium, from the House of Herakleidon. Constantine succeeded his father as emperor of the Byzantine Empire in 668, and early in his reign he succeeded in checking the Arab advance at the siege of Constantinople. He employed Greek fire at the 677 Battle of Syllaeum, a great Byzantine naval victory, and he routed the Arabs in 678. This siege was a major obstacle to the Muslims' conquest of the Byzantines, but ill health ruined his campaign against the First Bulgarian Empire, which ended in defeat at the Battle of Ongal in 680. In 685 he died of dysentery.